The Plant Cell Cycle

1
The Plant Cell Cycle

• Chapter 3

2

• Nucleus
• DNA
• Replication
• Cytoskeleton

3

The plant cell
Cell wall
CHLOROPLAST
CHLOROPLAST
Plasma membrane
MITOCHONDRIUM
NUCLEUS
MITOCHONDRIUM
MITOCHONDRIUM
CYTOSOL
CHLOROPLAST
CHLOROPLAST
MITOCHONDRIUM
Notes 1) cytosol is the same as cytoplasm
2) not all of the plant cell structures and
organelles are shown
4
one pore

• Nucleus
• Ovoid or irregular shaped
• Surrounded by double membrane (nuclear envelope)

nuclear envelope
0.2 µm
1 µm
lipid bilayer facing the nucleoplasm
lipid bilayer facing the cytoplasm
nuclear envelope
pore complex that spans both bilayers
Fig. 3-8, p. 37
5
Structure of Phospholipids and Glycolipids

• Hydrophilic
• Hydrophobic

6
Structure of Phospholipids and Glycolipids
7
Central dogma of Molecular Biology
DNA
TRANSCRIPTION
REPLICATION
RNA

TRANSLATION
mRNA
Ribosome
protein
8
Nucleolus production center for ribosomes
nuclear envelope
Nucleolus (rDNA, rRNA, ribosomal proteins, etc)
Chromosome
Early Prophase cell
9
Structure of DNA
10
A nucleosome consists of part of a DNA
molecule looped twice around a core of histones
(chromosomal proteins).
core of histone molecules
Fig. 3-9a, p. 37
11
Immerse a chromosome in saltwater and it loosens
up to a beads-on-a-string organization.
The string is one DNA molecule. Each bead
is a nucleosome.
Fig. 3-9b, p. 37
12
At a deeper level of structural organization,
the chromosomal proteins and DNA are organized
as a cylindrical fiber (again a helical
structure).
Fig. 3-9c, p. 37
13
At times when a chromosome is most condensed
(during Mitosis), the chromosomal
proteins interact, which packages loops of
already coiled DNA into a supercoiled array
(two additional helical organizations). Such a
tightly packaged DNA molecule is more easily
moved around compared to when it would be a long
loose thread (important during cell division)
Fig. 3-9d, p. 37
14
old
new
new
old
Fig. 2-18, p. 26
15
Cytoskeleton

• Structures in cytoskeleton
• Microtubules
• Motor proteins
• Microfilaments
• Specialized proteins connect microtubules and
  microfilaments to other organelles
• Connections thought to coordinate many cell
  processes

16
Cell Cycle
17
some cells leave the cycle
pre-DNA synthetic phase or gap phase
G1
cytokinesis
telophase
CELL
DNA synthesis phase
anaphase
Mitosis (M)
Interphase
metaphase
S
CYCLE
prophase
G2
some cells leave the cycle
premitosis phase
Note Interphase includes G1, S and G2 phases
Fig. 3-15, p. 43
18
Principal Control Point Hypothesis
control point
G1
M
S
control point
G2
Fig. 3-16, p. 44
19
A
B
C
band of microtubules
microtubules
nucleus
cell wall
cytoplasm
Fig. 3-18, p. 45
Formation of the preprophase band of microtubules
in meristematic cells A) Section at right
angles to the plane of the future cell plate
shows a cross section of
microtubules. B) Section in the plane of the
future cell plate shows microtubules encircling
the nucleus. C) Three-dimensional
drawing of A and B.
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Mitosis

• Four phases
• Prophase
• Metaphase
• Anaphase
• Telophase

21
Mitosis
d
a
c
e
b
cell plate
nuclear envelope
pole
spindle fiber
nucleolus
kinetochore
chromosome
Early Prophase Late Prophase Metaphase Late
anaphase Telophase
Fig. 3-19, p. 46
22
The roles of microtubules in mitosis
Fig. 3-17, p. 45
Visualization of tubulin (component of
microtubules) during mitosis.
23
Cell division in Plants versus Animals

• Animal cells do not have a cell wall
• Because plant cells have cell walls, the
  direction of cell division is a major determinant
  of overall plant development (cells are caught in
  a rigid structure and cannot reorganize after
  cell division has been completed). The
  direction/orientation of cell division is
  controlled by plant hormones.

24
Cell division in Plants versus Animals

• Animal cells do not form a preprophase band (PPB)
  
• During Telophase
• - in plants a cell plate is formed at the
  start of cytokinesis (direction of cell plate
  formation depends on hormone action via effects
  on PPB formation)
• - in animals the cell pinches in the middle to
  form two cells, no cell plate is formed.